1. Field of the Invention
The present invention pertains to a steckel mill that includes multiple coil furnace units respectively positioned upstream and downstream of an adjustable roller assembly through which a slab of metal is repeatedly passed in order to produce a progressively thinned and elongated metal sheet and, more particularly, to a combustion system for supplying a combustible mixture to each of the coil furnace units and for exhausting combustion products therefrom.
2. Discussion of the Prior Art
Rolling mills are commonly used for producing elongated metal sheets for various applications. In general, such rolling mills receive a slab of metal which is heated and is caused to pass between at least one pair of rollers of a roller assembly in order to thin and lengthen the metal slab. In certain known types of rolling mills, the slab is serially passed through various roller assemblies in a heated state. Each of these roller assemblies have associated spacings through which the metal slab passes which are progressively made smaller such that the slab is continually thinned as it passes through the rolling mill until an elongated metal sheet is produced. The elongated metal sheet can then be wrapped by means of a coiler for various uses.
Due to the number of and required spacing between the various roller assemblies in such a rolling mill, it has also been heretobefore proposed to produce an elongated metal sheet from a metal slab by utilizing a reverse rolling or steckel mill. FIG. 1 schematically illustrates a typical milling operation incorporating a steckel mill. This milling system, generally indicated at 1, receives a supply of metal from a continuous casting machine 5. Instead of continuous casting machine 5, a slab of metal can also be introduced into the through a heating furnace 9 and, if necessary, through a roughing roller-type mill unit 11. In some applications, roughing roller-type mill 11 is made reversible such that the slab or metal can be passed therethrough various times in order to obtain a slab having a certain thickness which is then passed to the steckel mill generally indicated at 15. Once the metal is elongated into a sheet in steckel mill 15, it proceeds to a cooling zone 18 and then is delivered over a guide roller 21 to a coiling device 24.
Steckel mill 15 typically includes first and second coil furnaces located within housings 28 and 29. Housings 28 and 29 each rotatably house a drum 32, 33 which are adapted to alternatively coil and uncoil a strip of metal indicated at 38. Metal strip 38, for instance, extends through an opening 40 in first housing 28, between rollers of a guide unit 42, between the rollers of a rolling mill assembly generally indicated at 46, through a second guide roller unit 48 and into second housing 29 through an opening 50. As is known in the art, the area through which strip 38 must pass within rolling mill assembly 46 is adjustable such that, as strip 38 is repeatedly passed through milling roller assembly 46 and alternatively coiled within housings 28 and 29, the thickness of strip 38 is systematically reduced commensurate with the elongation of strip 38. In order to maintain strip 38 in a flexible state for coiling and to enable strip 38 to be thinned out as it is passed through milling roller assembly 46, each housing 28 and 29 includes a coil furnace as discussed above to heat strip 38.
For this purpose, known steckel mills generally incorporate a plurality of burners which operate at a temperature in the order to 2000.degree.-3000.degree. F. The temperature of the waste gas or combustion products associated with such a steckel mill is often greater than 2000.degree. F. Currently, in the operation of known steckel mills, this flow of combustion products is merely exhausted into the atmosphere. This results in an extreme waste of energy and does not represent an efficient combustion system.
Therefore, in the art of steckel mills, there exists a need for a combustion system wherein at least a portion of the heat generated for heating of the metal passing through the steckel mill is recouped and utilized to increase the overall efficiency of the milling operation. There also exists a need in the art for an overall combustion system which assures an adequate and controlled combustion mixture to each of the coil furnaces incorporated in the steckel mill while providing for an economical and efficient manner of exhausting the combustion products produced during operation of the steckel mill.